Generally, vacuum systems for manufacturing integrated circuits on wafers are known. A vacuum system typically includes a centralized vacuum chamber, called a transfer chamber, for transferring wafers from a wafer cassette to one or more process chambers. The entire system, including the transfer chamber, load lock chambers and process chambers, is referred to as a cluster tool. A vacuum system may also typically have some kind of subsystem, such as a mini-environment, for delivering wafers to one or more load lock chambers and the into the transfer chamber where the wafers can be moved into one or more process chambers. After the wafers are processed, they are moved back through the load lock chamber and into wafer cassettes where the wafers can be moved to the next system for additional processing.
A vacuum processing system has various operating parameters, conditions and functions that are carried out by the various chambers within the system and the devices within and connected to these chambers. Such devices may be valve door actuators, heaters, vacuum pumps, vacuum valve actuators, gas valve actuators, temperature meters, pressure meters, wafer position sensors, door position sensors, robot motors, and a whole host of other devices that may be used in a vacuum processing system. Some of the functions or possible conditions or states of these and other devices make it impossible or dangerous for some other devices or parts of the system to perform their functions or to be in certain conditions or states.
For example, a transfer chamber typically has a removable lid. When this lid is removed, gases may escape from the transfer chamber into ambient air or vice versa. Process chambers attached to the transfer chamber, however, may be kept at a vacuum while the transfer chamber's lid is open, so a valve door that seals a valve opening between the transfer chamber and process chamber must be closed to prevent loss of the vacuum. Additionally, the process chamber may be using a toxic gas to perform its process, and the toxic gas may be harmful if it were to escape into ambient air. Therefore, when the lid of the transfer chamber is removed, it is important for the transfer chamber to lock out the valve door actuator from removing the door from the valve opening, so the toxic gas won't escape. The signals that a vacuum system uses to prevent such a disastrous occurrence are called interlocks. Interlock signals are sent between devices, or subsystems to prevent certain functions or conditions.
Another example of an interlock requirement when the transfer chamber lid is open is that the gas flow to the chamber should be turned off. Additionally, any vacuum line to the chamber should be turned off. If the chamber has a heater, it should be turned off, too.
Another interlock example is that if an over-temperature condition is detected in a chamber, then any heater in that chamber should be turned off. Likewise, if cooling water flow to a chamber is stopped, then the heater should be turned off, since the chamber may, otherwise, soon unacceptably heat up.
In still another interlock example, if a pump for a chamber has failed, then the gas flow to the chamber should be turned off.
There are many other examples of interlock requirements known to the vacuum processing industry.
The interlock signals are not sent directly from a device that generates an interlock to a device that receives the interlock. Instead, two or more of the generated interlocks are hardwired together to create a single combined interlock output that is then sent to the receiving devices. Thus, space within the system is economized. For example, a system that has six generated interlock signals may combine them into just two interlock output signals for sending to the receiving devices. The interlocks may be combined in this manner because many of the receiving devices will have the same response to the different interlock signals, as illustrated in the above examples.
An interlock signal typically is generated by a mechanical interlock switch associated with a particular device. For example, a chamber has a switch that is tripped by the chamber's lid when the lid closes, so when the lid opens, the switch opens, providing an interlock signal that the lid is open. Where needed, a chamber also has a thermostat switch that opens to provide an interlock signal indicating that the temperature has become too hot in the chamber. A system has a switch that opens to provide an interlock signal indicating a failed impedance matching box, which cancels the imaginary portion of the impedance of a chamber in order to match it with the impedance of the generated RF signal. The system also has a pressure-sensitive switch that opens to provide an interlock signal indicating that the pressure has become greater than 1/2 atmosphere in a chamber.
The inputs provided to the hardwired interlock circuitry are single lines from each interlock switch providing a voltage signal, such as +24V, when the switch is closed or providing an open circuit when the switch is open. The interlock input signals are hardwired to a series of relay switches. The relay switches are activated by the voltage signal to pass a signal that activates an output relay switch. When activated, the output relay switch sends an output voltage signal on a single line as the output provided by the hardwired interlock circuitry. When all of the interlock switches are closed, then the generated voltage signal will close all of the relays in the series, thus providing the output relay with the signal to close it, and the output line will carry the output voltage signal. When any one of the interlock switches is open, then the corresponding relay switch in the series will not receive the voltage to activate it, so the output relay will not receive the signal to close it, and the output line will not carry the output voltage signal, but rather will present an open circuited line.
A problem with this method of combining interlock signals is its lack of flexibility. Since the generated interlocks are hardwired together, there is no way to reconfigure the combinations. Thus, a device that doesn't have the exact same combination of interlock requirements as those that are hardwired together will have to accept a combined interlock signal that includes more than the device's actual requirement for generated interlock signals. It is not possible to reconfigure any of the combined interlock signals to provide only those generated signals that the device needs, so the device may receive an interlock that it doesn't need. This event may cause the device to shut down when it doesn't need to. Powering the device back up to operating conditions may cause a delay in the overall system processing. For example, if the device is a heater, then it will have to return to operating temperature before processing can continue.
Another problem with interlock systems is the lack of a means to defeat an interlock so it won't interfere during troubleshooting or testing of a vacuum system. In such a situation, an operator may want to turn on only a portion of the vacuum system in order to test its operation, but without the interference of another part. For example, under normal operating conditions, the removal of a chamber lid may cause an interlock to turn off a heater inside the chamber. If the operator wants to see how the heater is working, then the operator may need to open the lid without turning off the heater, so the operator may observe the operation of the heater. This technique is not possible under current designs for combining interlocks.
Another problem with interlock systems is the lack of any feedback to the operator showing where the interlock signal came from. The operator sometimes must go through an extensive troubleshooting procedure to determine which device generated the interlock signal, especially when several generated interlock signals are hardwired through one combined output.
Thus, a need has arisen for an electrical interlock system that permits reconfiguration of the interlock combinations and permits an interlock to be defeated and provides interlock feedback to an operator.